Lens is a transparent, biconvex, crystalline structure placed between iris and the vitreous in a saucer-shaped depression, the patellar fossa. The lens is a crystalline structure that is avascular and is devoid of nerves and connective tissue
It consists of three distinct part:
Lens capsule
Anterior lens epithelium, and
Lens substance or lens fibres
The aqueous humour is a transparent, watery fluid similar to plasma, but containing low protein concentrations. It is secreted from the ciliary epithelium, a structure supporting the lens
Corneal metabolism
1. o Cornea requires energy for normal metabolic activities as well as for maintaining transparency and dehydration o Energy is generated by the breakdown of glucose in the form of ATP o Most actively metabolizing layer are epithelium and endothelium o Sources of nutrients : o Oxygen : mainly from atmosphere through tear film , with minor amount supplied by the aqueous and limbal vasculature o Glucose , amino acid, vitamins and other nutrients supplied to cornea by aqueous humor o Glucose also derived from glycogen stores in corneal epithelium o Epithelium consumes O2 10 times faster then stroma
2. o Three process or pathways – o Pentose shunt (Hexose monophosphate shunt) –occurs both in hypoxic and normoxic condition o Glycolysis (Embden meyerhof pathway) –anaerobic process , glucose / glycogen converted to pyruvate yeilding 2 ATPs o TCA or krebs or citric acid cycle- aerobic condition pyruvate is oxidized to yield 36 ATP, water, CO2.
3. o In normal conditions all the glucose consumed by the cornea o Glucose mostly come from aqueous humor o The rate of glucose consumption by the whole cornea is approx. 100 microgram/hr/cm2. o 1 mol. of glucose will be converted to the pyruvic acid and produced 2 molecules lactic acid and 2 mol. of ATP o In the krebs cycle, 1 mol. of glucose will utilize the pyruvic acid and O2 to produced 36 mol. ATP o Epithelium and endothelium will consume the oxygen
4. o The pentose phosphate pathway is used to metabolize five carbon sugars; one ATP and 2 NADH molecules are produced from oxidation of one glucose molecule o Produced intermediates for nucleic acid synthesis and some amino acids o This process will happen in hypoxic or normoxic condition o The purpose of glucose metabolism through the pentose shunt is the production of NADPH
The aqueous humour is a transparent, watery fluid similar to plasma, but containing low protein concentrations. It is secreted from the ciliary epithelium, a structure supporting the lens
Corneal metabolism
1. o Cornea requires energy for normal metabolic activities as well as for maintaining transparency and dehydration o Energy is generated by the breakdown of glucose in the form of ATP o Most actively metabolizing layer are epithelium and endothelium o Sources of nutrients : o Oxygen : mainly from atmosphere through tear film , with minor amount supplied by the aqueous and limbal vasculature o Glucose , amino acid, vitamins and other nutrients supplied to cornea by aqueous humor o Glucose also derived from glycogen stores in corneal epithelium o Epithelium consumes O2 10 times faster then stroma
2. o Three process or pathways – o Pentose shunt (Hexose monophosphate shunt) –occurs both in hypoxic and normoxic condition o Glycolysis (Embden meyerhof pathway) –anaerobic process , glucose / glycogen converted to pyruvate yeilding 2 ATPs o TCA or krebs or citric acid cycle- aerobic condition pyruvate is oxidized to yield 36 ATP, water, CO2.
3. o In normal conditions all the glucose consumed by the cornea o Glucose mostly come from aqueous humor o The rate of glucose consumption by the whole cornea is approx. 100 microgram/hr/cm2. o 1 mol. of glucose will be converted to the pyruvic acid and produced 2 molecules lactic acid and 2 mol. of ATP o In the krebs cycle, 1 mol. of glucose will utilize the pyruvic acid and O2 to produced 36 mol. ATP o Epithelium and endothelium will consume the oxygen
4. o The pentose phosphate pathway is used to metabolize five carbon sugars; one ATP and 2 NADH molecules are produced from oxidation of one glucose molecule o Produced intermediates for nucleic acid synthesis and some amino acids o This process will happen in hypoxic or normoxic condition o The purpose of glucose metabolism through the pentose shunt is the production of NADPH
INTRODUCTIONThe clear fluid filling the space in front of the eyeball between lens and cornea.The aqueous humour supplies nutrition and removes waste from the clear structure in the anterior eye(cornea and lens)The balance between aqueous production and outflow determines the intraocular pressure.
INTRODUCTION
The clear fluid filling the space in front of the eyeball between lens and cornea.
The aqueous humour supplies nutrition and removes waste from the clear structure in the anterior eye(cornea and lens)
The balance between aqueous production and outflow determines the intraocular pressure.
The tear film constitutes Three layers :- An outermost lipid (oily) layer An aqueous (watery) layer that makes up 90% of the tear film volume; and A mucin layer that coats the corneal surface.
3. To form smooth optical surface on cornea. To keep the surface of cornea & conjunctiva moist It serve as lubricant It transfer oxygen Provide antibacterial action Wash debris out It provides a pathway for WBC in case of injury
4. Functions of lipid layer Retards evaporation of tear film Prevents the overflow of tears
5. Function of Aqueous Layer Flushes, buffers and lubricates the corneal surface Delivers oxygen and other nutrients to the corneal surface Wash out debris Delivers antibacterial enzymes and antibodies such as lysozyme.
6. Functions of Mucin Layer Spreads tears over corneal surface. Protects the cornea against foreign substances . Makes corneal surface smooth by filling in surface irregularities
Vitreous humour
1. Vitreous Humour
2. General features Vitreous humour is an inert ,transparent , colourless, jellylike, hydrophilic gel that serves the optical functions and also acts as important supporting structures for the eyeball. The vitreous cavity is bounded by anteriorly by the lens and ciliary body and posteriorly by the retina Its weighs nearly 4g Vitreous is an extacellular material composed of approximately 99 per cent water
3. Structure The vitreous body is the largest and simplest connective tissue present as a single piece in the human body Divided into three parts- 1. The hyaloid layer or membrane 2. The cortical vitreous and 3. The medullary vitreous
1. Introduction Gross anatomy Layers Blood supply, drainage and nerve supply
2. INTRODUCTION • Sclera forms posterior 5/6th of external tunic , connective tissue coat of eyeball. • it continues with duramater and cornea • Its whole surface covered by tenon’s capsule • Anteriorly covered by- bulbar conjunctiva • Inner surface lies in contact with choroid • With a potential suprachoroidal space in between
3. Equa THICKNESS OF SCLERA
4. • Thickness varies with individual, with age • Thinner- children, elder, F> M • Thickest posteriorly • Gradually becomes thinner when traced anteriorly • Thin at insertion of extraocular muscle
INTRODUCTIONThe clear fluid filling the space in front of the eyeball between lens and cornea.The aqueous humour supplies nutrition and removes waste from the clear structure in the anterior eye(cornea and lens)The balance between aqueous production and outflow determines the intraocular pressure.
INTRODUCTION
The clear fluid filling the space in front of the eyeball between lens and cornea.
The aqueous humour supplies nutrition and removes waste from the clear structure in the anterior eye(cornea and lens)
The balance between aqueous production and outflow determines the intraocular pressure.
The tear film constitutes Three layers :- An outermost lipid (oily) layer An aqueous (watery) layer that makes up 90% of the tear film volume; and A mucin layer that coats the corneal surface.
3. To form smooth optical surface on cornea. To keep the surface of cornea & conjunctiva moist It serve as lubricant It transfer oxygen Provide antibacterial action Wash debris out It provides a pathway for WBC in case of injury
4. Functions of lipid layer Retards evaporation of tear film Prevents the overflow of tears
5. Function of Aqueous Layer Flushes, buffers and lubricates the corneal surface Delivers oxygen and other nutrients to the corneal surface Wash out debris Delivers antibacterial enzymes and antibodies such as lysozyme.
6. Functions of Mucin Layer Spreads tears over corneal surface. Protects the cornea against foreign substances . Makes corneal surface smooth by filling in surface irregularities
Vitreous humour
1. Vitreous Humour
2. General features Vitreous humour is an inert ,transparent , colourless, jellylike, hydrophilic gel that serves the optical functions and also acts as important supporting structures for the eyeball. The vitreous cavity is bounded by anteriorly by the lens and ciliary body and posteriorly by the retina Its weighs nearly 4g Vitreous is an extacellular material composed of approximately 99 per cent water
3. Structure The vitreous body is the largest and simplest connective tissue present as a single piece in the human body Divided into three parts- 1. The hyaloid layer or membrane 2. The cortical vitreous and 3. The medullary vitreous
1. Introduction Gross anatomy Layers Blood supply, drainage and nerve supply
2. INTRODUCTION • Sclera forms posterior 5/6th of external tunic , connective tissue coat of eyeball. • it continues with duramater and cornea • Its whole surface covered by tenon’s capsule • Anteriorly covered by- bulbar conjunctiva • Inner surface lies in contact with choroid • With a potential suprachoroidal space in between
3. Equa THICKNESS OF SCLERA
4. • Thickness varies with individual, with age • Thinner- children, elder, F> M • Thickest posteriorly • Gradually becomes thinner when traced anteriorly • Thin at insertion of extraocular muscle
An enzyme is a substance that acts as a catalyst in living organisms, regulating the rate at which chemical reactions proceed without itself being altered in the process. The biological processes that occur within all living organisms are chemical reactions, and most are regulated by enzymes
The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. The cornea, with the anterior chamber and lens, refracts light, with the cornea accounting for approximately two-thirds of the eye's total optical power.
Small amounts of vitamins are required in the diet to promote growth, reproduction, and health. Vitamins A, D, E, and K are called the fat-soluble vitamins, because they are soluble in organic solvents and are absorbed and transported in a manner similar to that of fats.
Water soluble vitamins include Vitamin C and the vitamin B complex: thiamin (B1), riboflavin (B2), niacin (B3), pantothenic acid (B5), Vitamin B6, biotin (B7), folic acid (B9), Vitamin B12. Vitamin A in its Beta-Carotene form is also water-soluble.
The tear film is a complex mixture of substances secreted from multiple sources on the ocular surface, including the lacrimal gland, the accessory lacrimal glands, the meibomian glands, and the goblet cells.
A picornavirus is a virus belonging to the family Picornaviridae, a family of viruses in the order Picornavirales. Vertebrates, including humans, serve as natural hosts. Picornaviruses are nonenveloped viruses that represent a large family of small, cytoplasmic, plus-strand RNA viruses with a 30-nm icosahedral capsid.
Poxviruses are brick or oval-shaped viruses with large double-stranded DNA genomes. Poxviruses exist throughout the world and cause disease in humans and many other types of animals. Poxvirus infections typically result in the formation of lesions, skin nodules, or disseminated rash.
Leptospirosis is a bacterial disease that affects humans and animals. It is caused by bacteria of the genus Leptospira. In humans, it can cause a wide range of symptoms, some of which may be mistaken for other diseases. Some infected persons, however, may have no symptoms at all.
The human immunodeficiency virus (HIV) is a lentivirus (a subgroup of retrovirus) that causes HIV infection and over time acquired immunodeficiency syndrome (AIDS).
Treponema is a genus of spiral-shaped bacteria. The major treponeme species of human pathogens is Treponema pallidum, whose subspecies are responsible for diseases such as syphilis, bejel, and yaws.
Haemophilus is the name of a group of bacteria. There are several types of Haemophilus. They can cause different types of illnesses involving breathing, bones and joints, and the nervous system. One common type, Hib (Haemophilus influenzae type b), causes serious disease. It usually strikes children under 5 years old
Moraxella is a genus of Gram-negative bacteria in the Moraxellaceae family. It is named after the Swiss ophthalmologist Victor Morax. The organisms are short rods, coccobacilli, or as in the case of Moraxella catarrhalis, diplococci in morphology, with asaccharolytic, oxidase-positive, and catalase-positive properties
Pseudomonas is a type of bacteria that can cause infections. Pseudomonas is a common genus of bacteria, which can create infections in the body under certain circumstances. There are many different types of Pseudomonas bacteria
Neisseria gonorrhoeae is the obligate human pathogen that causes the sexually transmitted disease (STD) gonorrhea. This Gram-negative diplococci/gonococci does not infect other animals or experimental animals and does not survive freely in the environment. The gonococcal infection occurs in the upper or lower tract, pharynx, ophthalmic area, rectum, and bloodstream. During the 1980’s gonorrhea was also referred to as “the clap” when public awareness was quite minimal. This was one of the venereal diseases prostitutes hoped to contract since it resulted in infertility by pelvic inflammatory disease (PID). As documentation, diagnostic testing, and public awareness improved, there has been a decline in incidence reports, however, it is still considered a very common infectious disease.
Meningococci are a type of bacteria that cause serious infections. The most common infection is meningitis, which is an inflammation of the thin tissue that surrounds the brain and spinal cord. Meningococci can also cause other problems, including a serious bloodstream infection called sepsis. In its early stages, you may have flu-like symptoms and a stiff neck. But the disease can progress quickly and can be fatal. Early diagnosis and treatment are extremely important. Lab tests on your blood and cerebrospinal fluid can tell if you have it. Treatment is with antibiotics. Since the infection spreads from person to person, family members may also need to be treated.
A vaccine can prevent meningococcal infections.
Diphtheria is an infection caused by the bacterium Corynebacterium diphtheriae. Diphtheria causes a thick covering in the back of the throat. It can lead to difficulty breathing, heart failure, paralysis, and even death. CDC recommends vaccines for infants, children, teens and adults to prevent diphtheria. The presentation consists of basic concepts regarding the bacteria and its infection. It has explanation in detail about signs and symptoms of Diptheria
Contraindications, Adverse reactions and ocular nutritional supplementsArun Geetha Viswanathan
utritional supplements comprise a great deal of the products available over the counter in most pharmacies. Although most vitamin supplements are relatively harmless—except for the fat soluble ones A, D, E, and K—they are not the only supplements available to patients. Some of these other, non-vitamin supplements can actually be harmful to patients and often they have been proven to be ineffective. This doesn’t mean that patients will stop taking them though, which in turn leaves the potential for contraindications of nutritional supplements with prescription-based drugs wide open.
Ageing is a gradual process that takes place over many decades. Most theories of ageing relate to impaired DNA replication and loss of cell viability and hence the viability of the body’s organs. Ageing is often accompanied by socioeconomic changes that can have a great impact on the nutritional needs and status of elderly individuals. The incidence of disability increases with ageing, with over a third of the elderly population limited by chronic conditions and unable to carry on normal daily living activity
Every component of the eye is vulnerable to damage from ROI, particularly retina. There are several reasons for the vulnerability of the retina, including high concentrations of polyunsaturated fatty acid (PUFA), constant exposure to visible light, high consumption of oxygen, an abundance of photosensitisers in the neurosensory retina and the RPE, the process of phagocytosis by the RPE which is known to generate hydrogen peroxide.
Carotenoids are class of fat soluble coloured pigments, found primarily in plants, where they play a critical role in the photosynthetic process. Two xanthophylls, lutein (L) and zeaxanthin (Z) accumulate at the macula where they make up macular pigment (MP). In the human eye, the MP optical density (MPOD) is not uniformly distributed across the retina
The increased availability of biomedical data, particularly in the public domain, offers the opportunity to better understand human health and to develop effective therapeutics for a wide range of unmet medical needs. However, data scientists remain stymied by the fact that data remain hard to find and to productively reuse because data and their metadata i) are wholly inaccessible, ii) are in non-standard or incompatible representations, iii) do not conform to community standards, and iv) have unclear or highly restricted terms and conditions that preclude legitimate reuse. These limitations require a rethink on data can be made machine and AI-ready - the key motivation behind the FAIR Guiding Principles. Concurrently, while recent efforts have explored the use of deep learning to fuse disparate data into predictive models for a wide range of biomedical applications, these models often fail even when the correct answer is already known, and fail to explain individual predictions in terms that data scientists can appreciate. These limitations suggest that new methods to produce practical artificial intelligence are still needed.
In this talk, I will discuss our work in (1) building an integrative knowledge infrastructure to prepare FAIR and "AI-ready" data and services along with (2) neurosymbolic AI methods to improve the quality of predictions and to generate plausible explanations. Attention is given to standards, platforms, and methods to wrangle knowledge into simple, but effective semantic and latent representations, and to make these available into standards-compliant and discoverable interfaces that can be used in model building, validation, and explanation. Our work, and those of others in the field, creates a baseline for building trustworthy and easy to deploy AI models in biomedicine.
Bio
Dr. Michel Dumontier is the Distinguished Professor of Data Science at Maastricht University, founder and executive director of the Institute of Data Science, and co-founder of the FAIR (Findable, Accessible, Interoperable and Reusable) data principles. His research explores socio-technological approaches for responsible discovery science, which includes collaborative multi-modal knowledge graphs, privacy-preserving distributed data mining, and AI methods for drug discovery and personalized medicine. His work is supported through the Dutch National Research Agenda, the Netherlands Organisation for Scientific Research, Horizon Europe, the European Open Science Cloud, the US National Institutes of Health, and a Marie-Curie Innovative Training Network. He is the editor-in-chief for the journal Data Science and is internationally recognized for his contributions in bioinformatics, biomedical informatics, and semantic technologies including ontologies and linked data.
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
Richard's aventures in two entangled wonderlandsRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
A brief information about the SCOP protein database used in bioinformatics.
The Structural Classification of Proteins (SCOP) database is a comprehensive and authoritative resource for the structural and evolutionary relationships of proteins. It provides a detailed and curated classification of protein structures, grouping them into families, superfamilies, and folds based on their structural and sequence similarities.
(May 29th, 2024) Advancements in Intravital Microscopy- Insights for Preclini...Scintica Instrumentation
Intravital microscopy (IVM) is a powerful tool utilized to study cellular behavior over time and space in vivo. Much of our understanding of cell biology has been accomplished using various in vitro and ex vivo methods; however, these studies do not necessarily reflect the natural dynamics of biological processes. Unlike traditional cell culture or fixed tissue imaging, IVM allows for the ultra-fast high-resolution imaging of cellular processes over time and space and were studied in its natural environment. Real-time visualization of biological processes in the context of an intact organism helps maintain physiological relevance and provide insights into the progression of disease, response to treatments or developmental processes.
In this webinar we give an overview of advanced applications of the IVM system in preclinical research. IVIM technology is a provider of all-in-one intravital microscopy systems and solutions optimized for in vivo imaging of live animal models at sub-micron resolution. The system’s unique features and user-friendly software enables researchers to probe fast dynamic biological processes such as immune cell tracking, cell-cell interaction as well as vascularization and tumor metastasis with exceptional detail. This webinar will also give an overview of IVM being utilized in drug development, offering a view into the intricate interaction between drugs/nanoparticles and tissues in vivo and allows for the evaluation of therapeutic intervention in a variety of tissues and organs. This interdisciplinary collaboration continues to drive the advancements of novel therapeutic strategies.
Slide 1: Title Slide
Extrachromosomal Inheritance
Slide 2: Introduction to Extrachromosomal Inheritance
Definition: Extrachromosomal inheritance refers to the transmission of genetic material that is not found within the nucleus.
Key Components: Involves genes located in mitochondria, chloroplasts, and plasmids.
Slide 3: Mitochondrial Inheritance
Mitochondria: Organelles responsible for energy production.
Mitochondrial DNA (mtDNA): Circular DNA molecule found in mitochondria.
Inheritance Pattern: Maternally inherited, meaning it is passed from mothers to all their offspring.
Diseases: Examples include Leber’s hereditary optic neuropathy (LHON) and mitochondrial myopathy.
Slide 4: Chloroplast Inheritance
Chloroplasts: Organelles responsible for photosynthesis in plants.
Chloroplast DNA (cpDNA): Circular DNA molecule found in chloroplasts.
Inheritance Pattern: Often maternally inherited in most plants, but can vary in some species.
Examples: Variegation in plants, where leaf color patterns are determined by chloroplast DNA.
Slide 5: Plasmid Inheritance
Plasmids: Small, circular DNA molecules found in bacteria and some eukaryotes.
Features: Can carry antibiotic resistance genes and can be transferred between cells through processes like conjugation.
Significance: Important in biotechnology for gene cloning and genetic engineering.
Slide 6: Mechanisms of Extrachromosomal Inheritance
Non-Mendelian Patterns: Do not follow Mendel’s laws of inheritance.
Cytoplasmic Segregation: During cell division, organelles like mitochondria and chloroplasts are randomly distributed to daughter cells.
Heteroplasmy: Presence of more than one type of organellar genome within a cell, leading to variation in expression.
Slide 7: Examples of Extrachromosomal Inheritance
Four O’clock Plant (Mirabilis jalapa): Shows variegated leaves due to different cpDNA in leaf cells.
Petite Mutants in Yeast: Result from mutations in mitochondrial DNA affecting respiration.
Slide 8: Importance of Extrachromosomal Inheritance
Evolution: Provides insight into the evolution of eukaryotic cells.
Medicine: Understanding mitochondrial inheritance helps in diagnosing and treating mitochondrial diseases.
Agriculture: Chloroplast inheritance can be used in plant breeding and genetic modification.
Slide 9: Recent Research and Advances
Gene Editing: Techniques like CRISPR-Cas9 are being used to edit mitochondrial and chloroplast DNA.
Therapies: Development of mitochondrial replacement therapy (MRT) for preventing mitochondrial diseases.
Slide 10: Conclusion
Summary: Extrachromosomal inheritance involves the transmission of genetic material outside the nucleus and plays a crucial role in genetics, medicine, and biotechnology.
Future Directions: Continued research and technological advancements hold promise for new treatments and applications.
Slide 11: Questions and Discussion
Invite Audience: Open the floor for any questions or further discussion on the topic.
Predicting property prices with machine learning algorithms.pdf
The Lens
1. Lens
Unit 3
Structure and Functions of Lens. Zonules.Biochemistry, Protein
fractions, Electrolytes, Dehydration and Transparency
2. Shape, transparency and Dimensions
• Lens is a transparent, biconvex, crystalline
structure placed between iris and the vitreous in
a saucer-shaped depression, the patellar fossa.
• To be more precise, the lens is an asymmetric
oblate spheroid
• The posterior surface of the lens capsule is in
intimate contact with the vitreous in this fossa
and is attached to it in a circular area with
ligamentum hyaloid capsular (Wiegert's ligament)
• Inside this circle, between hyaloid face and the
lens capsule is a small cavity or potential space
called as retrolental or Berger's space.
3. Shape, transparency and Dimensions
• Equatorial diameter of the lens, about 6.5 mm at birth, increases to 9-10 mm in the second decade and then
remains almost constant
• Thickness (axial or anteroposterior diameter) varies with age between 3.5 mm (at birth) and 5 mm (at extreme
of age)
4. Shape, transparency and Dimensions
• Weight of lens varies with age
• At birth, the weight is about 65 mg, which increases rapidly to about 125 mg by the end of first year
• It then increases approximately 2.8 mg/year until the end of first decade reaching about 150 mg
• Thereafter the rate of increase slows to reach a weight of approximately 260 mg at 70-80 years of age
• In males, the lens weighs more than the aged matched females, with a mean difference of 7.9 +2.47 mg.
At birth
65 mg
First year
125 mg
10th year
150 mg
70th - 80th year
260 mg
2.8 mg/year Slow rate
5. • Surfaces: It has two surfaces. The anterior surface, less convex than the posterior, is the segment of a sphere
whose radius averages 10 mm (8-14 mm)
• The posterior surface, more curved than the anterior, presents a radius of about 6 mm (4.5-7.5 mm)
• Equator: These two surfaces of lens meet at the equator, which is almost circular and has a rippled or undulated
appearance
Shape, transparency and Dimensions
6. Poles
• The centre of the anterior and posterior surface is called as the anterior pole and posterior pole,
respectively
• The anterior pole is about 3 mm from the back of cornea
• Refractive index of the lens is 1.39 (nucleus 1.42, cortex 1.38)
• Its refractive power is about 16 -17 dioptres
Shape, transparency and Dimensions
7. • Accommodative power varies with age, being 14-16 D at birth; 7-8 D at 25 years of age and 1-2 D at 50
years of age
• Colour of the lens also changes with age. A transparent lens in infants and young adults is colourless,
acquires a definite yellow tinge after about 30 years of age and appears amber coloured in old age.
• Consistency of the lens cortex differs from the nucleus; the former being softer than the latter.
Shape, transparency and Dimensions
8. Lens is a crystalline structure that is avascular and is devoid of nerves and connective tissue
It consists of three distinct part:
1. Lens capsule
2. Anterior lens epithelium, and
3. Lens substance or lens fibres
Structure of lens
9. • Lens capsule is a thin, transparent, hyaline collagenous membrane which surrounds the lens completely
• capsule is highly elastic but does not contain any elastic tissue
• Capsule is secreted by the basal cell area of the lens epithelium anteriorly and by the basal area of the
elongated fibres posteriorly
• Produced continuously through life, the lens capsule is the thickest base in membrane in the body
Structure of lens: Lens capsule
10. • Capsule thickness varies according to the age and is not consistent through its extent
• It is thicker anteriorly than posteriorly and at the equator than the poles, being thinnest at posterior
pole
• On light microscopy, the capsule appears as a homogenous structure
• on ultramicroscopic examination, it shows a lamellar appearance.
• Each lamella contains fine filaments
Structure of lens: Lens capsule
11. • In true exfoliation of the lens capsule, superficial zonular lamella
of the capsule splits off from the deeper layer
• Lens capsule is composed principally of type IV collagen and 10%
glycosaminoglycans
• It contains enzyme, ATP and glycolytic intermediates but cannot
be considered to have an independent metabolism
• There are chemical and antigenic similarities between the lens
capsule and basement
Structure of lens: Lens capsule
12. • single layer of cuboidal nucleated epithelial cells and lies deep to the anterior capsule extending upto
equatorial lens bow
• These cells contain all the organelles found in a typical epithelial cell
• Lens epithelial cells contain three cytoskeletal elements, microfilaments (actin), intermediate filaments
(vimentin) and microtubules (tubulin)
Structure of lens: Anterior lens epithelium
13. • Almost all the metabolic, synthetic and transport processes of the lens occur in this layer
• In the equatorial region, these cells become columnar, are actively dividing and elongating to form new
lens fibres throughout life
• There is no posterior epithelium, as these cells are used up in filling the central cavity of the lens vesicle
during development of the lens
Structure of lens: Anterior lens epithelium
14. The anterior lens epithelium can be divided into three zones:
1. Central zone
• It consists of cuboidal cells which are polygonal in flat section
• These cells are approximately 10 um high and 15 um wide
• Their nuclei are round and located slightly apically. These cells are
stable and their number slowly reduces with age
• Under normal circumstances, these cells do not mitose, but can do
so in response to a wide variety of injurious insults including uveitis
• During injury repair, epithelial cells are elongated; resembling
fibroblasts and can pile up to 10 layers thick under the capsule.
Structure of lens: Zones of lens epithelium
15. The anterior lens epithelium can be divided into three zones:
2. Intermediate zone
• It consists of comparetively smaller and more cylindrical cells located
peripheral to the central zone
• Their nuclei are round and central
• These cells mitose occasionally
Structure of lens: Zones of lens epithelium
16. The anterior lens epithelium can be divided into three zones:
3. Germinative zone
• It consists of columnar cells which are most peripheral and located
just pre equatorial
• Nuclei of these cells are flattened and lie in the plane of cell axis
• Cells of the germinative zone are actively dividing to form new cells
which migrate posteriorly to become lens fibres
• This process continues throughout life
• These cells are extremely susceptible to irradiation
Structure of lens: Zones of lens epithelium
18. Formation
• The epithelial cells elongate to form the lens fibres
• At first, the lens fibres are formed from the posterior epithelium which runs from posterior to anterior to fill
the lens vesicle
• But later on, the lens fibres are derived from the cells of the equatorial region of the anterior epithelium
Structure of lens: Lens substance or lens fibers
19. • These cells divide, elongate and differentiate to
produce long, thin, regularly arranged lens fibres that
constitute the bulk of the lens
• Successively, the new lens fibres are laid on the older
deeper fibres
• The superficial (new) fibres are nucleated with
elongation of the cell; the nuclei assume a relatively
more anterior position
• As the new fibres are laid down, the anterior shifted
nucleus forms a line convex forward at the equator,
known as lens or nuclear bow
Structure of lens: Lens substance or lens fibers
20. Structure of lens fibres
• On cross-section, the lens fibres are almost hexagonal in shape and are bound together by the ground
substance
• The cytoplasm of the cells of the superficial bow region and the newly formed lens fibres contain a
nucleus, mitochondria, Golgi apparatus, rough endoplasmic reticulum, and polysomes
Structure of lens: Lens substance or lens fibers
21. • The ribosomal content of the newly formed lens fibres is more
than the epithelial cells indicating an elevated protein synthesis
• The nuclei of the lens fibres are present temporarily and
disappear later on
• Thus the cytoplasm of the older lens fibres is devoid of nuclei, is
homogenous and granular with very few organelles
• There are interlocking processes between cells (ball-and-socket
and tongue-and groove interdigitations) with zonulae
occludentes present
• Both desmosomes and tight junctions are absent from the
mature lens fibres, although desmosomes are found between
elongating fibres
Structure of lens: Lens substance or lens fibers
22. • It is interesting to note that the interdigitations are less
complicated in the superficial zone of the lens; and this may
permit moulding of the lens shape during accommodation
Structure of lens: Lens substance or lens fibers
23. Structural arrangement of the lens fibres
• The initial fibres forming the fetal nucleus just surrounding the
embryonic nucleus are arranged in such a way that they
terminate with two Y-shaped suture on the anterior (upright Y)
and the posterior (inverted Y) surface of the lens
Structure of lens: Lens substance or lens fibers
24. Structural arrangement of the lens fibres
Structure of lens: Lens substance or lens fibers
• Later in gestation and following birth, the growth of
the lens sutures is much more irregular
• Instead of simple Y-sutures, more complicated
dendritic patterns are observed due to asymmetrical
fibre growth
• The formation of sutures enables the shape of the lens
to change from spherical to a flattend biconvex sphere
A) Embryonic
B) Adult lens
fibre
arrangement
25. Zonal arrangement of the lens fibres
Structure of lens: Lens substance or lens fibers
• The lens fibres are formed throughout life and are
arranged in zones that delineate the various periods of
development of the lens
• This stratification is due to optical differences between
the older, more sclerotic regions of the central lens
and the newer, more transparent peripheral areas
• In an adult, the lens fibres are arranged compactly as
nucleus and cortex of the lens
26. Zonal arrangement of the lens fibres
Structure of lens: Lens substance or lens fibers
A. Nucleus.
• It is the central part containing the oldest fibres. It
consists of different zones
• Embryonic nucleus is its innermost part (formed at 1
to 3 months of gestation)
• The embryonic nucleus contains the original primary
lens fibre cells that are formed in the lens vesicle
27. Zonal arrangement of the lens fibres
Structure of lens: Lens substance or lens fibers
• Outside the embryonic nucleus, successive nuclear
zones of secondary lens fibres are laid down
concentrically, encircling the previously formed
nucleus as the development proceeds, and depending
upon the period of formation, are called:
• Fetal nucleus (corresponding to lens from 3 months of
gestation till birth)
• Infantile nucleus (corresponding to lens from birth to
puberty) and
• Adult nucleus (corresponding to the lens in adult life)
Note. The size of the embryonic and fetal nuclei remains
constant while that of adult nucleus is always increasing
28. Zonal arrangement of the lens fibres
Structure of lens: Lens substance or lens fibers
29. The ciliary zonules
• The ciliary zonules (zonules of Zinn or
suspensory ligament of lens) consist essentially
of a series of fibres which run from the ciliary
body and fuse into the outer layer of the lens
capsule around the equatorial zone
• Thus, they hold the lens in position and enable
the ciliary muscle to act on it
30. The ciliary zonules: Structure
• The zonular fibres are transparent, stiff and not elastic. Each zonular fibre has a diameter of about 0.35 to
1.0 micro meter
• It is composed of microfibrils with a diameter varying from 8-40 nm
• Zonular fibres are composed of glycoproteins and mucopolysaccharides and are similar in structure to the
microfibrils of the elastic fibres
• Their susceptibility to hydrolysis by a chymotrypsin has been used to advantage in intracapsular cataract
surgery
• Structurally, three different types of zonular fibres have been described
1. First type fibres. These are thick, about 1 m in diameter, wavy and usually lie near the vitreous
2. Second type fibres. These are thin and flat.
3. Third type fibres, These are very fine and run a circular course.
32. Arrangement of Zonular Fibres
A. Main fibres of the ciliary zonules
• The main fibres of the ciliary armies which bind the lens
with the ciliary body, depending upon their arrangement
can be classified into the following four groups
1. Orbicular Posterior capsular fibres
• These are the most posterior and innermost zonular fibres
• These take origin from the ora serrata, pass anteriorly in
close contact with the anterior limiting layer of the
vitreous and are inserted together with hyaloid capsular
ligament in the posterior capsule of the lens
• Structurally, they are second type fibres.
33. Arrangement of Zonular Fibres
2. Orbicular Anterior capsular fibres
• These are the thickest and strongest (structurally of first type)
zonular fibres
• They arise from the pars plana of ciliary body (orbicularis
ciliaris), pass anteriorly to get inserted anterior to the equator
• By the supporting (auxiliary) fibres, they are attached to the
valleys and sides of the ciliary processes
3. Cillioposterior capsular fibres
• These are the most numerous zonular fibres
• They arise mainly from the valleys and a few from the sides of
the ciliary processes, pass posteriorly and get inserted on the
posterior capsule anterior to the insertion of the orbiculo-
posterior capsular fibres.
34. Arrangement of Zonular Fibres
4. Cillioequatorial fibres
• These fibres arise from the valleys of the ciliary processes
and pass almost directly inward to be inserted at the equator
• They occupy the whole of the interval between the anterior
and posterior group of fibres
• These are third type of fibres
• These are present in abundance in youthful eyes and tend to
disappear and become sparse with advancing age
B. Auxiliary fibres
• The auxiliary or supporting fibres provide strength to main
fibres by anchoring the individual portions of zonules
• These also help to hold the various portions of the ciliary
body together
35. 34% Protein65% Water
Biochemical composition of lens
Water constitutes about
65% of the lens wet
weight
Of the solids, the highest is
protein which constitutes about
34% of the total weight of an
adult lens
lipids, inorganic ions,
carbohydrates, ascorbic
acid, glutathione and
amino acids
36. }65% Water
Biochemical composition of lens: Lens water
• Lens is a relatively dehydrated organ, cortex being more hydrated than nucleus
• maintained by an active sodium pump that resides within the membrane of the cell, in the lens epithelium and
in each lens fibre
• Fischer suggested that out of this about 80% is free while remaining is bound water
• A small portion of the lens water is located in the extracellular space
• Low amount of water in the lens is a natural consequence of the need for having a refractive index quite
different from that of the watery fluids at the two optical interfaces of the lens
• The normal human lens does not show significant alteration in hydration with age
80% free water
37. Proteins
Soluble,
Albumin
Insoluble,
Crystallin
Biochemical composition of lens: Proteins
• Protein content of the lens is higher than that of any other organ in the body
• The physical state of proteins is an important factor for the maintenance of transparency
• Morner for the first time classically divided the proteins of crystalline lens of cattle into
an insoluble fraction called albumin and the soluble fraction called crystallins
• The soluble fraction has three components namely alpha-, beta- and gamma crystallin
• The three crystallins can be separated by precipitation at different pH, by salting out, by
electrophoresis or by running through cellulose column
38. Biochemical composition of lens: Proteins
Krause studied the various protein fractions in the lens as follows:
Proteins Insoluble albumin 12.5%
Alpha – Crystallin 31.7%
Beta – Crystallin 53.4%
Gamma – Crystallin or albumin
1.5%
Mucoproteins
0.8 %
Nucleoproteins
0.07%
Soluble
fraction
39. Biochemical composition of lens: Proteins
Proteins
• few minor proteins reported in the lens are glycoprotein, phosphoprotein, lipoprotein and fluorescent
proteins
• cortex contains more soluble proteins than nucleus which contains more insoluble proteins
• The cortex of the young lens practically contains no albuminoid, whereas the nucleus of old lens is composed
of almost entirely of albuminoid
• alpha-crystallin and albuminoid are immunologically similar
Alpha Crystallin
(Soluble)
Albuminoid protein
(Insoluble)
Age ↑
40. Biochemical composition of lens: Proteins
Soluble proteins
• The lens crystallins make up the bulk of refractive fibres of the lens and are considered structural proteins
• synthesis of soluble proteins takes place in the equatorial part and on the surface of lens
• The newly formed fibres contain very little or no albuminoid
• A part of the soluble lens proteins may be formed in deeper lens fibres, at least in those which contain nuclei
• The high concentration of crystallins and the gradient of refractive index are responsible for the refractive
properties of the lens
• The short range order of these proteins ensures that the lens remains transparent
41. Biochemical composition of lens
Alpha-crystallin
• the highest molecular weight and at alkaline pH it has the greatest positive
charge
• Average molecular wt of about 106
• composed of several polypeptides held together by non-covalent forces
• The molecular wt of the A chains is 19,500 and of the B chains 22,500
• The A chains contain one thiol group per chain while B chains appear to
contain no thiol group
• alpha-crystallins are polymers and consist approximately of 50 monomers
• They are the largest crystallin
42. Biochemical composition of lens
Beta-crystallins.
• This fraction of lens proteins is a heterogenous group of proteins with molecular
wt from 5 x 104 to 2 x 105
• The beta-crystallins contain many polypeptide chains, some of which appear to be
present in aggregates
• Shapiro has reported that this protein group contains three different polypeptide
chains of the molecular weights of 21000, 23000 and 29000
• They also have a relatively high thiol content and might have disulphide linkages
43. Biochemical composition of lens
Gamma-crystallin
• These are composed of monomers only
• This fraction constitutes about 60% of soluble lens proteins in young rat and dog
fish
• As the lens ages, there is a progressive and significant decrease in the relative
concentration
• Gamma-crystallin level is high in nucleus and low in cortex, especially in young
cortex
• These are the smallest crystallins.
44. Biochemical composition of lens
Insoluble proteins
• The chief insoluble protein is albuminoid - 12.5% of total protein
• Molecular wt - 3,70,000
• Found as a mixture - it is only partly digested by urea - extracted by soidic aqueous solution
• The amino acid composition of this protein is similar to alpha crystallin
• In human lens, most of the albuminoid is urea Soluble and appears to be derived from the alpha-crystallins
45. Biochemical composition of lens
Other lens proteins
• Glycoproteins are a group of proteins to which sugars are covalently bound
• They are primarily associated with the lens cell membrane and are of considerable importance
• They also contribute to the intercellular ground substance.
• The lens cortex contains considerably more glycoproteins than the nucleus
• Some other rare lens proteins include nucleoproteins, phosphoproteins, lipoproteins and fluorescent
proteins
46. Biochemical composition of lens: Amino acids
Amino Acids
Proteinogenic
alanine, leucine, glutamic acid, aspartic acid, glycine, valine,
phenylalanine, tyrosine, serine, isoleucine, lysine, histidine,
methionine, proline, threonine and arginine
Non - proteinogenic
taurine, alpha-amino butyric acid, ornithine, 1-methyl-histidine,
3-methyl-histidine and homo-carnosine
• lens contains all the amino acids present in any other tissue except tryptophan, cysteine and possibly
hydroxy-proline
• Concentration of each amino acid is higher in the lens as compared to aqueous humour vitreous humour
leading to a conclusion that they are actively transported into the lens
47. Biochemical composition of lens: Amino acids
• An active process is necessary to ensure that protein synthesis is not limited by the availability of amino
acids
• the free amino acid pool is quite characteristic and constant for similar animals
• amino acid concentration of lens is not appreciably affected by ageing, fasting or feeding a protein-free diet
• unaltered level of amino acids in lens may be a result of balance of protein synthesis and catabolism on one
hand and amino acid excretion, uptake by lens and the synthesis and breakdown of amino acids
48. Biochemical composition of lens: Carbohydrates
Carbohydrates
Free
glucose, fructose, and glycogen
Derivatives sorbitol, inositol, ascorbic
acid, gluconic acid and glucosamine
49. Biochemical composition of lens: Carbohydrates
Glucose
• The glucose level - vary from 20-120 mg%
• reported still lower concentration of glucose in
lens in various species
• The lenticular glucose has its source in aqueous
humour
• The level of glucose in lens is 1/10th of
aqueous, where glucose concentration has
been found to be 100 mg%.
Fructose
• It is produced from glucose in the crystalline
lens
• Concentration of fructose varies considerably in
many species
• Its concentration also varies with age
• 6 mg - 14th day & 50 mg-100 mg at 550th day
(Rats)
50. Biochemical composition of lens: Carbohydrates
Glycogen
• Only traces of glycogen have been found in
mammalian lenses
• Concentration varies with age and the region of lens
• localised principally in the nucleus where it appears
to replace gamma-crystallin
• normally present there to functionally to increase
refractive index
• It is located as a thin layer of intracellular granules,
surrounding the nuclei of epithelial cells
Sorbitol
• Found in normal lens of several species
• 17 mg/100 g fresh lens of rabbit
Inositol
• found in the lens of several species
• Its function is unknown although it may possibly be
involved in the metabolism of phospholipids
51. Biochemical composition of lens: Lipids
• 2.5% of wet weight
• cholesterol, various phospholipids such as cephalexin, isolecithin, sphingomyelin and glycerides
• human lens had lipids in two forms, a free form and a bound form as lipoproteins
• The proteolipids constitute 2% of the wet weight of lens and that 65% of lenticular lipids are bound to
proteins
• lipids are most abundant in epithelial cells in children and in the cortex in adults
• it may function as a lubricating cement substance
• lipid content (cholesterol) increases with age especially in nucleus while the glycerides decrease
• Similar changes occur in cataract where lecithin is abundant and cholesterol is found as crystals
• In cataracts the concentration of free lipids increases and lipoprotein decreases.
52. Biochemical composition of lens: Electrolytes
Potassium
• It is the predominant cation in lens
• Its concentration in fresh human lens has been
reported to vary between 114 and 130 mEq/kg lens
matter
• The levels are higher than in any other eye tissue
• This high level is probably a result of the unusually
large proportion of intracellular space in lens
Sodium
• Its concentration in lens is about 10 to 50% of the
potassium
• In human lens, the sodium concentration is about 14-
25 mEq/kg lens water
• There is some variation in these levels between
species and a marked regional variation in the
concentration of sodium, which is more than twice in
the superficial cortex as compared to central nucleus.
53. Biochemical composition of lens: Electrolytes
Calcium
• normal young lens has one of the lowest of
all tissue calcium levels
• A mean value of 0.14 mg/mg dry weight is
reported for human lenses.
Anions
• The main anions of the lens are chloride,
bicarbonate, phosphate and sulphates
• Phosphate is the predominant anion in the
lens, comprising nearly half the ash
• The level reported for the total phosphate is
240 mg/ 100 g and for inorganic phosphate
25 mg/100 g in young calf lens
54. Biochemical composition of lens: Glutathione
• The content of glutathione in the lens depending on the species and the method used for its estimation
has been reported to vary from 3.5 to 5.5 mm/g wet weight of the lens
• The level of glutathione in the lens is also known to be altered with the age of the individual
• Its concentration falls with advancing age
• This decrease in the level of glutathione with advancing age is relative and not absolute
• It is because of the increase in the wet weight of the lens with age
• The lens is constantly exposed to attack by oxidative agents; indeed there is a high level of hydrogen
peroxide in normal aqueous and peroxidase activity is also present in the lens itself
55. Biochemical composition of lens: Glutathione
• Several enzyme systems are available to minimize or buffer the effects of oxidants, including catalase,
superoxide dismutase, glutathione peroxidase and glutathione-S-transferase
• The lens contains high levels of glutathione with the highest concentration in the epithelium
• Catalase and low levels of superoxide dismutase have also been identified in lens epithelium concluding
that these systems are also probably important
• Glutathione is also important in protecting thiol groups in proteins, especially cation transporting
membrane proteins in the lens, which additionally accounts for its unusual high concentration in this
tissue
• More than 95% of glutathione is in the reduced state
56. Biochemical composition of lens: Ascorbic Acid
• Mean value of ascorbic acid in an adult man is 30 mg/100 gm of the wet weight of the lens
• In the aqueous humour, ascorbic acid is actively transported to a concentration some 15 times greater
than that in plasma
Though the ascorbic acid content of the lens is even greater than that of aqueous humour, it is neither
synthesized nor actively transported into the lens
• Its accumulation within the lens might be explained by assuming that a portion of ascorbic acid is protein
bound
• the conversion between ascorbic acid and the oxidized form, dehydroascorbic acid, might be coupled with
other oxidation reduction systems in the lens